Effect of predominant methanogenic flora on the outcome of lactose breath test in irritable bowel syndrome patients

Background: The relationship between hydrogen and methane production is a possible confounding factor in the interpretation of H-2 breath tests (HBT), but is usually disregarded for the interpretation of HBT and, in most instances, only H-2 excretion is measured. The present study was designed to evaluate the effect of predominant fasting methane CH4 or H-2 production on the outcome of lactose HBT, in a large, homogeneous series of adult patients with irritable bowel syndrome (IBS). Patients and methods: A lactose HBT was performed in 237 IBS patients with predominant fasting methane production (CH4>H-2), recording the outcome of the test, amount of gas excreted and occurrence of clinical symptoms. Data were compared to those of 237 age- and sex-matched IBS patients with low fasting CH4 excretion. Results: The test was positive in 124 predominant CH4 producers (52.3%) (PMP), as compared to 201 (84.8%) low methane producers (LMP) (P < 0.0001). Peak hydrogen concentration and area under the curve of H-2 were significantly (P < 0.001) lower, and the occurrence of symptoms during the test less frequent, in PMP vs LMP patients. During the test, CH4 excretion doubled in 57/113 (50.4%) patients with negative HBT, and in 49/124 (39.5%) with positive HBT. Conclusions: Patients with predominant fasting methane production excrete less H-2 than LMP, after an oral load of lactose. The lower prevalence of severe lactose intolerance in PMP, as well as lower incidence of symptoms during the test, is, indeed, related to lower and slower H-2 excretion. The assumption that H-2 excretion is an effective means of quantifying the amount of malabsorbed carbohydrates is questionable in PMP. Methane-producing patients likely have a higher 'false negative' rate as compared to LMP after an oral load of lactose. Nonetheless, as symptoms are related to the amount of gas produced in the colon, HBT identifies patients with 'lactose intolerance', irrespective of the presence of lactose malabsorption, and helps in predicting the effect of lactose-restricted diet.